number nth should always return number at nth(1), like ruby sass does
implement length and nth for boolean
add support for empty lists
fix paren usage in if node

one test still fails
fix bug introduced with 26d196f678cc3c5a2fdf2347a4c3c41c6b178a36

variables set in mixin where not correctly passed
remove custom compassIf function

- doesn't work correctly, string 'false' gets interpreted as true
- there is already a working if implementation which this one overrides
Allow colon and dot in SassScriptFunction to fix MS filters.
Fix test whitespace.
merge tests